This invention relates to an innovative means and method for the placement of welded wire mesh normally used in the construction of poured mesh-reinforced concrete slabs. The term "slabs" refers to flat formations of concrete for use in paving, walks, drives, parking areas, and other similar items of concrete slab construction.
Mesh reinforcement, commonly referred to as "temperature" reinforcement, usually is steel woven and welded wire mesh which, when embedded in poured concrete slabs, tends to hold the concrete in place and reduce the tendency of the concrete to crack after it has hardened or "set." Concrete slabs have a tendency to crack unless expansion joints are provided, ordinarily spaced at intervals of twelve to twenty feet, depending upon the thickness of the slab. The reinforcing material distributes expansion and contraction action so that if cracking occurs, many imperceptible "hair-line" cracks are developed rather than one or several visible ones as often happens when reinforcement is improperly located within the slab thickness, or in the case of unreinforced concrete.
The normal or usual method of installing mesh reinforcement is to unroll it onto the area to receive the slab, or if the mesh is supplied in a flat shape, to place the mesh on the area prior to pouring the wet and plastic concrete.
After pouring an area of concrete to the approximate thickness of the slab desired, and while the concrete is in workable condition, the mesh is raised to the desired position, which should be midway of the slab thickness, and in the case of a four inch slab, about two inches above the bottom of the slab.
This manual method of positioning the mesh is usually accomplished by the use of a hooked or bent wire or any type of tool with which it is possible to engage a section or portion of the wire mesh in order to raise it into the wet concrete. This raising or lifting is usually done by workmen who must walk in the wet concrete, as described and shown in an article entitled "Control of Random Cracking in Exterior Residential Flatwork," Part II, appearing at page 511, in the Dec. 1971 issue of Concrete Construction.
The procedure described above is a haphazard and unsatisfactory method of positioning the mesh reinforcing within the slab. It is ineffective and inefficient in that:
(a) Portions of the mesh which remain at the bottom of the slab are wasted since they have no reinforcing value; PA1 (b) Varying heights of the mesh location within the slab may actually have a damaging effect upon the slab due to the different stresses induced, i.e., portions of the mesh near the bottom of the slab may be considered to be in tension, while portions of the mesh near the top of the slab would be in compression.
These conditions occurring one or more times within a given width and/or length of a slab conceivably would induce stresses working against each other and weaken the slab to the extent of causing cracking. In view of this possibility the installation of wire mesh by the usual method may be more harmful than beneficial, as far as reinforcement is concerned.
In view of the above reasons, it follows that by positively and accurately controlling the location of the reinforcing mesh at the approximate center, or within the middle third of the thickness of the slab, a reinforced slab conforming to design requirements will be obtained.
In order to overcome the objections referred to above, it is an object of the present invention to provide means and a method of controlling the uniform and proper location of the reinforcing material, such as wire mesh, in the preparation of concrete slabs and thereby obtain a slab having the desired strength and resistance to cracking.